Having worked in corporations, there always seems to be two groups of people. I don't know what to call them, but I'll just call them group 1 and 2. If the whole group is led by certain group 1 members, then group 2 members are often excluded for no apparent reason. Leaders from group 2 include everyone. There are no obvious physical or personality characteristics I can identify as a source of separation. I have some ideas, but I don't want to speculate.
Changing leadership (in your case, have another child or maybe an appropriate adult ultimately in charge) or having someone taking the role of coach seems to be the only ways I know of to solve this. I am a group 2 type and take on the role of coach if I see this happening. It is not that I am assigned the role, I just can't keep my mouth shut when I see these things happening. To avoid conflict, I don't make it overly obvious I am doing this though. One trick I have learned to get out information to the group 1 types is to put it in the form of a question.
I figured this was an appropriate opportunity to put out one of my less likely to be believed observations. As good a time as any to have an idea get summarily rejected without real consideration (couldn't resist the opportunity for humour).
<nodding> Yes.
Some of this technique can be TAUGHT, though, as a means of working productively with difficult people. If you allow the OTHER person to 'approve' your idea (ie-- via asking it as a 'question') then you stand a much better chance of gaining cooperation with people who have a need for control.
"I think that we should _________."
versus
"Hmmm. I might be off-track, here, but has anyone mentioned _____________?"
I also like to use "Explain please" statements-- but this requires something that many gifted children REALLY struggle with--
a willingness to look as though they are NOT the EXPERT."Is there a reason why we can't try ________?"
"I don't think that I understand __________ here; can someone explain it to me?"
The questioning and self-effacing statements defuse potential 'social challenge' in idea presentation, making it easier for socially dominant (or controlling) people to hear and acknowledge them. Those strategies are REALLY effective as communication tools when used well.

(It took me a long time to learn these things. I'm a naturally pretty assertive person, but that did NOT work well as a communication strategy when I was both a young faculty member and a female one in a department of older men. So my choices were to adapt to be more effective or to simmer with resentment about not being heard. Easy decision.

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